1. Field of Invention
The present invention relates to test assemblies for calibration of gas analyzers.
2. Description of Prior Art
It has been required for environmental reasons, among others, to monitor combustion gases. This is done to determine that the levels of certain constituent gases exiting a flue or stack have been kept within acceptable limits. A common technique used for carbon monoxide level measurement has been an optical monitor using infrared light. A beam of infrared light was sent from an optical transmitter through the exiting gases in the flue to an optical receiving station. The transmitter and receiver were mounted on opposite sides of the gas flue, usually at a fairly elevated position. The amount of carbon monoxide in the exiting flue gases affected the passage of infrared light, and detected variations in light levels thus indicated changing carbon monoxide concentrations.
As time passed, it was necessary to periodically calibrate the monitor. Calibration required that both the transmitter and receiver of the monitor be removed from the flue and taken to a test bench or laboratory for testing. A calibration was then made by placing a sealed disc, containing a known sample concentration of carbon monoxide, between transmitter and receiver. The gas concentration readings could then be checked against the known sample concentration and adjustments made to the monitor electronics as needed.
Prior art patents for gas concentration monitoring, so far as is known, have required that a test probe be inserted into the flue or chamber where gas presence is being analyzed. Examples include U.S. Pat. Nos. 4,094,187; 4,205,550; 4,206,630 and 4,279,142. Calibration of these types of monitors necessitated removal of the test probes from the flues or chambers. A further patent, U.S. Pat. No. 4,322,964, related to a valving arrangement for controlling and regulating flow of both stack gas and calibration gas through a calibration system.